Diffusion Combustion during Interaction of a Supersonic Round Microjet of Air with a Coaxial (Coflowing Ring) Jet of Hydrogen

The results of experimental investigations of the features of diffusion combustion during the interaction of a round supersonic microjet of air in the center and a coaxial (coflowing ring) jet of hydrogen. Such combustion is accompanied by a number of new phenomena: the formation of a cone-shaped flame near the nozzle сutoff, the locking of the combustion region in this cone, the presence of small-scale supersonic cells in the resulting flow, and the formation of laminar sections and their turbulization.

The Delay in Cavity Formation in the Intrusive Mode of Coalescence of a Freely Falling Drop with a Target Liquid

The dynamics of a cavity formed in the intrusive mode of coalescence of a freely falling drop flowing smoothly into a liquid have been traced for the first time by the methods of photo and video registration. The cavity begins to form when the bottom part of the drop submerges, when the fluid coalescence line contracts to the center of the flow, and, simultaneously with the annihilation of the drop surface, the surface of the target liquid is restored. In this case, the orientation of ligaments (thin trickles), formed in the vicinity of the contact line changes. At the initial phase, they are directed outward and distribute the transmitted momentum and energy of the drop over the entire surface of the intrusion. Retraction of the coalescence line holds the transmitted energy and momentum of the drop in the contact patch. If the kinetic energy of the falling drop noticeably exceeds the potential surface energy, the cavity begins to form at the initial contact of the fluids and deepens in the course of the entire coalescence process, capturing the drop matter.

A β Ti–20Nb–10Ta–5Zr Alloy with the Surface Structured on the Micro- and Nanoscale

This alloy is shown to be homogeneous (Ti 65%, Nb 20%, Ta 10%, Zr 5%). A change in the elemental composition is observed only in the layer close to the surface with a thickness of about 100 nm. The alloy surface is depleted in titanium (∼20%) and enriched in tantalum (∼20%). There is also a large amount of oxides on the surface (∼50%). The alloy is single-phase with a β-Ti-type crystal lattice (cubic system, space group Im3m). The alloy has yield strength of about 550 MPa and a tensile strength of about 700 MPa. The Young’s modulus is about 50 GPa. The relative elongation of the alloy is about 1.4%. On a microscale, folds and longitudinal comb-like structures up to 0.5 μm in height are found on the surface of wires and plates made of the Ti–20Nb–10Ta–5Zr alloy. When analyzing nanotopology, it is found that, even between comb-like structures or at their tops, there are irregularities up to 100–150 nm in height.